1. Technical Field
This disclosure relates generally to rotary drill bits. In particular, a drill bit of the present disclosure may be employed, e.g., in a drilling apparatus for drilling a borehole into the earth.
2. Description of Related Art
Often when drilling a borehole into the earth, a down-hole drilling motor is suspended from the lower end of a drill string. A drilling fluid may be transmitted through the drill string and circulated through the drilling motor to induce rotation of a drill bit, and the rotating drill bit engages a subterranean rock formation to produce a borehole therein. In some instances, directional drilling may be desirable, i.e., it may be desirable to produce a borehole that deviates from a vertically oriented path.
Some mechanisms employed for this purpose include a bent subassembly, integrated in the down-hole drilling motor, typically between the power section of the motor and the bearing assembly. A bent subassembly generally includes a bent or bendable structural component that supports the bearing assembly, and a drill bit at its lower end, at a slight angle to the direction of the drill string above the bent subassembly. The bent subassembly may define a fixed angle, or the angle may be adjustable. When it is desired to drill in a generally straight path, the entire drill string may be continuously rotated from the surface, and the motor may or may not be activated. When it is desired to cause the path of the borehole to diverge in a given direction, continuous rotation of the drill string is stopped, and the drill string, bent subassembly, motor and bit are oriented to in the desired direction of divergence. The upper part of the drill string is held in this position and the down-hole motor is started. This causes the borehole to diverge in the desired direction. A minimum turning radius of these mechanisms may be limited in part by a “bit-to-bend” length that may be generally described as the distance from a fulcrum point of the bent subassembly to leading face of the drill bit.
Another type of drilling apparatus that may be employed for directional drilling is a rotary steerable system (RSS). Generally, a rotary steerable system provides some mechanism for steering the drill bit in a desired direction, usually without requiring continuous rotation of the drill string from the surface to be stopped. Many rotary steerable systems include a mechanism for providing a radial or sideways-direction force relative to the lower end of the drill string to steer the drill bit on a path that diverges from a straight path.
The drill bits employed for vertical drilling and/or directional drilling may need to be replaced for a number of reasons including wear or breakage of the surfaces contacting the subterranean rock formation. Often, drill bits are provided with a threaded interface, or another repeatable coupling, on a shank portion thereof to permit decoupling of a broken or worn drill bit from a lower portion of the motor, and replacement with a new or refurbished bit.
Advancements made in the design and usage of drill bits have made it possible to extend the expected life of a bit beyond the expected need for the bit for a particular application or project. Thus, it is now possible for a user to rent a drill bit for use on a project, and return the bit for subsequent use by another user on another project. This increase in the usable life of drill bits has affected the design considerations made in the manufacture of drill bits for down-hole drilling motors.